In general, a rotary vane-type compressor has a series of working chambers each defined by an outer peripheral surface of a rotor, side faces of two succeeding vanes, an inner peripheral surface of a housing and an inner surface of a side plate. Coolant gas is introduced into a working chamber while the volume of that working chamber is increasing. Then, the introduced coolant gas begins to be compressed and is discharged while the volume of that working chamber is decreasing. In a conventional compressor of this type, an end face of the rotor is closely juxtaposed with the inner surface of the side plate in order to avoid longitudinal movement of the rotor. However, according to the present inventors' observation, there is a drawback, in that material may deposit between the end face of the rotor and the inner surface of the side plate in this type of conventional compressor. The present inventors also have found the reason for this problem, as described below.
In order to avoid generation or reduction of a gap between the rotor, the housing and the side plate caused by thermal expansion thereof, all of the elements of a conventional compressor of this type usually are made of the same material, e.g., cast iron. Accordingly, the contact between the end face of the rotor and the inner surface of the side plate is a contact between bodies of the same material, and the tendency that a deposition is caused when there is contact between the same materials is known. It must be noted that merely changing of the material of the rotor or the side plate causes other problems, i.e., the thickness of the gap between the rotor and the side plate cannot be controlled.
In order to solve the above problem, at first, the present inventors tried making the width of the vanes longer than that of the rotor for using contacting only between the axially opposite end faces of the vanes and the inner surface of the side plate. Since the vanes can be made of a different metal material from that of the rotor deposition of material between the vanes and the side plate is not easily caused. Also, longitudinal movement of the rotor is controlled by the contact between the vanes and the side plate. However, in the modified compressor just described, the stress (total force/total area) on the side faces of the vanes becomes high because the area of the side faces of the vanes is small. And that makes the power needed for rotating the rotor high.